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Typical analyses of otolith microchemistry use calcium, a major constituent, as an internal standard, setting its value as a constant and ignoring any potential variations. In fact, patterns do occur in otolith Ca deposition, as can be observed either by repeating the analysis, by creating two-dimensional maps of Ca, or both. Here we present evidence of Ca variations in fish otoliths from analyses using synchrotron-based scanning X-ray fluorescence microscopy, electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). 2-D maps of otoliths created with LA-ICP-MS indicate that Ca is elevated where especially Zn and P are low, and vice versa, suggesting that spatial variations in protein deposition may affect concentrations of Ca. We encourage others to examine Ca concentrations in their biomineralized samples to check for variations, using LA-ICP-MS and other methods. 

Abstract. Inclusion–host elastic thermobarometers are widely used to determine the pressure and temperature (P–T) histories of metamorphic rocks. Complex metamorphic P–T paths can affect the pressures that develop in host–inclusion systems. There are limited experimental studies that investigate how changing P–T conditions may re-equilibrate or “reset” residual pressures of inclusions. To evaluate re-equilibration of the quartz-in-garnet (QuiG) elastic thermobarometer, we performed single-, two-, and three-stage isothermal experiments. In the first stage of the experiments, oxide starting materials hydrothermally crystallised to grow garnet crystals with quartz inclusions between 700 and 800 °C and 1.0 and 3.2 GPa with constant P–T conditions for 48 h. In the second and third stage of the experiments, we isothermally changed pressure by 1.0 to 1.2 GPa for durations up to 38 d. We used Raman spectroscopy to measure strain-induced changes to the 128, 207, and 465 cm−1 Raman bands of quartz inclusions to determine the inclusion pressures (Pinc) and entrapment pressures (Ptrap) at the experimental temperature. The multi-stage experiments show that elasticity primarily controlled changes to Pinc values that occur from Ptrap through quenching to room conditions and that Pinc values measured at room conditions along with elastic modelling can be used to accurately calculate Ptrap. Quartz Pinc values in two-stage experiments re-equilibrated to give Pinc values between P1 and P2. The three-stage isothermal experiments show that the observed changes to inclusion pressures are reversible along different P–T paths to restore the re-equilibrated Pinc values back to their original entrapment isomeke at Ptrap. For rocks that underwent protracted metamorphism along complicated P–T paths, the re-equilibration experiments and viscoelastic calculations show that QuiG may underestimate maximum Ptrap conditions. 

Abstract New results that employ Zr‐in‐rutile thermometry (ZiR) and quartz‐inclusion‐in‐garnet (QuiG) barometry constrain the P–T conditions of garnet formation in blueschists and eclogites from the island of Syros, Greece. QuiG barometry reveals that garnet from different regions across the island formed at pressures ranging from 1.1 to 1.8 GPa and ZiR thermometry on rutile inclusions in garnet constrains the minimum temperature of garnet formation to have been 475–550°C. Most importantly, there is no systematic difference in the conditions of garnet formation from different regions across the island and these results are nearly identical to those obtained from the islands of Sifnos and Ios, Greece. A model is proposed whereby the rocks from all three islands were initially metamorphosed along a relatively shallow geotherm of around 11°C/km to a depth of around 45 km and were then subjected to metamorphism along a geotherm of around 7–8°C/km, which could have been caused by either an increase in the dip of the subduction zone or an increase in the rate of subduction. Garnet formed along this steeper geotherm was accompanied by the release of significant H₂O from the breakdown of chlorite over a duration of 1 Ma or less based on thermal and diffusion modeling. It is concluded that rocks from Syros, Sifnos and Ios all followed a similar, roughly counter‐clockwise prograde P–T path and that the present outcrop configuration is largely due to a complex exhumation history. 

Here, we use multi-method thermobarometric analyses (thermodynamic modelling, quartz in garnet barometry, Raman spectroscopy of carbonaceous material (RSCM) thermometry, and titanium in biotite thermometry) from samples throughout two transects in the Northwestern Tethyan Himalaya (TH) to constrain the pressure-temperature conditions of the basal TH. Peak metamorphic conditions from the basal TH indicate anomalously high pressures relative to the paleogeothermal gradients recorded along the two transects, suggesting non-lithostatic pressure conditions at the base of the Tethyan Himalaya. The TH fold-thrust belt comprises a deformed Neoproterozoic-Cretaceous section of sedimentary rocks that record the early stages of deformation of the Himalayan orogen. In the northwestern Himalaya, rocks at the base of the TH are metamorphosed and are useful for reconstructing the thermal evolution of the Himalaya during initial stages of crustal thickening. RSCM thermometry on samples along the Pin Valley and Sutlej Valley transects of the TH suggest a continuous ~1500 °C/GPa thermobarometric gradient through the entire TH section. These samples are from a continuous ~10-12 km-thick TH section in which the stratigraphically highest units are undeformed, fossil-bearing sedimentary rocks. Assuming lithostatic pressure, the basal TH is expected to record peak pressure-temperature (P-T) conditions of ~0.4-0.5 GPa and ~600 °C. However, quartz-in-garnet (QuiG) barometry and titanium-in-biotite thermometry of samples from the basal TH indicate peak P-T conditions of 0.94 ± 0.25 GPa and ~600°C, suggesting a paleo-geothermal gradient of 870-500 °C/GPa. These data constitute unexpectedly high peak pressure conditions along the basal TH. Possible explanations for these anomalously high basal TH pressures include pre-Himalayan metamorphic assemblages preserved in the TH resulting in erroneous Himalayan peak P-T estimates, or regional non-lithostatic pressure along the basal TH during Himalayan orogenesis. Thermobarometric work on samples from different stratigraphic levels of the basal TH in the Sutlej Valley is in progress to determine paleo-geothermal gradient continuity both across- and along-strike of the orogen. 

The Tethyan Himalaya (TH) fold-thrust belt comprises a deformed Neoproterozoic-Cretaceous section of sedimentary rocks that record the early stages of deformation of the Himalayan orogen. In the northwestern Himalaya, rocks at the base of the TH are metamorphosed and are useful for reconstructing the thermal evolution of the Himalaya during initial stages of crustal thickening. Here, we present results of multi-method thermobarometry (thermodynamic modelling, Si in white mica barometry, quartz in garnet barometry, raman spectroscopy of carbonaceous material (RSCM) thermometry) on metasedimentary samples from two transects across the TH, with apparently continuous stratigraphy separated along strike of the orogen by ~40 km. Samples from the Pin Valley region record peak pressure-temperature (P-T) conditions of 0.4-0.5 GPa, 600 °C, suggesting a paleo-geothermal gradient of 30-40 °C/km. These samples are from the base of a continuous ~10-12 km-thick TH section in which the stratigraphically highest units are undeformed, fossil-bearing sedimentary rocks. RSCM thermometry on samples from stratigraphically higher levels of the TH suggest a continuous ~40 °C/km geothermal gradient through the entire TH section in the Pin Valley region. In contrast, previous thermobarometric studies from the Sutlej Valley ~40 km to the east report peak P-T conditions of 0.7-0.8 GPa, 600-650 °C, suggesting a paleo-geothermal gradient of 20-25 °C/km. Our new data indicate significant along-strike variation in peak P-T conditions and paleo-geothermal gradients at the base of the TH. Possible explanations for this along-strike thermobarometric discrepancy include: 1) pre-Himalayan metamorphic assemblages preserved in the TH resulting in erroneous Himalayan peak P-T estimates, 2) along-strike structural differences that resulted in differential burial and exhumation during Himalayan orogenesis, or 3) non-lithostatic pressure during orogenesis. Thermobarometric work on samples from different stratigraphic levels of the basal TH in the Sutlej Valley is in progress to determine paleo-geothermal gradient continuity both across- and along-strike of the orogen. 

Abstract Garnet–kyanite–staurolite assemblages with large, late porphyroblasts of amphibole form garbenschists in Ordovician volcaniclastic rocks lying immediately south of the Pearya terrane on northernmost Ellesmere Island, Canada. The schist, which together with carbonate olistoliths makes up the Petersen Bay Assemblage (PBA), displays a series of parallel isograds that mark an increase in metamorphic grade over a distance of 10 km towards the contact with Pearya; however, a steep, brittle Cenozoic strike-slip fault with an unknown amount displacement disturbs the earlier accretionary relationship. The late amphibole growth, probably due to fluid ingress, is clear evidence of disequilibrium conditions in the garbenschist. In order to recover the P–T history of the schists, we construct isochemical phase equilibrium models for a nearby garnet–mica schist that escaped the fluid event and compare the results to quartz inclusion in garnet (QuiG) barometry for a garbenschist and the metapelitic garnet schist. Quartz inclusions are confined to garnet cores and the QuiG results, combined with Ti-in-biotite and garnet–biotite thermometry, delineate a prograde path from 480 to 600°C and 0.7 to 0.9 GPa. This path agrees with growth zoning in garnet deduced from X-ray maps of the spessartine component in garnet. The peak conditions obtained from pseudosection modelling using effective bulk composition and the intersection of garnet rim with matrix biotite and white mica isopleths in the metapelite are 665°C at ≤0.85 GPa. Three generations of monazite (I, II and III) were identified by textural characterization, geochemical composition (REE and Y concentrations) and U–Pb ages measured by ion microprobe. Monazite I occurs in the matrix and as inclusions in garnet rims and grew at peak P–T conditions at 397 ± 2 Ma (2σ) from the breakdown of allanite. Monazite II forms overgrowths on matrix Monazite I grains that are oriented parallel to the main schistosity and yield ages of 385 ± 2 Ma. Monazite III, found only in the garbenschist, is 374 ± 6 Ma, which is interpreted as the time of amphibole growth during fluid infiltration at lower temperature and pressure on a clockwise P–T path that remained in the kyanite stability field. These results point to a relatively short (≈12 Myr) Barrovian metamorphic event that affected the schists of the PBA. An obvious heat source is lacking in the adjacent Pearya terrane, but we speculate it was large Devonian plutons—similar to the 390 ± 10 Ma Cape Woods granite located 40 km across strike from the fault—that have been excised by strike-slip. Arc fragments that are correlative to the PBA are low grade; they never saw the heat and were not directly involved in Pearya accretion.